Spontaneous resolution of cryptogenic organizing pneumonia: Observational study.

Cryptogenic organizing pneumonia (COP) is an idiopathic interstitial pneumonia generally requiring steroid therapy, and spontaneous resolution has been reported in patients with mild disease. However, evidence supporting the need for COP treatment is poor. Therefore, we investigated the characteristics of patients with spontaneous resolution. We retrospectively collected data from 40 adult patients who were diagnosed with COP through bronchoscopic examination at Fukujuji Hospital from May 2016 to June 2022. Sixteen patients who improved without steroid therapy (the spontaneous resolution group) and 24 patients who required steroid therapy (the steroid therapy group) were compared. Patients in the spontaneous resolution group showed a lower C-reactive protein (CRP) concentration (median 0.93 mg/dL [interquartile range [IQR] 0.46-1.91] vs median 10.42 mg/dL [4.82-16.7], P < .001), a higher lymphocyte ratio (median 21.7% [18.2-25.2] vs median 13.3% [8.8-19.8], P = .002), and a longer duration from symptom onset to diagnosis of COP (median 51.5 days [24.5-65.3] vs 23.0 days [17.3-31.8], P = .009) than those in the steroid therapy group. Within 2 weeks, all patients in the spontaneous resolution group showed relief of symptoms and alleviated radiographic findings. The area under the receiver operating characteristic (ROC) curve was 0.859 (95% confidence interval [CI]: 0.741-0.978) in CRP. When we arbitrarily determined the cutoff values, including CRP levels of ≤3.79 mg/dL, the sensitivity, specificity, and odds ratio were 73.9%, 93.8%, and 39.8 (95% confidence interval: 4.51-1968.9), respectively. Only 1 patient in the spontaneous resolution group showed recurrence but did not require steroid therapy. Conversely, 4 patients in the steroid therapy group showed recurrence and were treated by an additional course of steroids. The characteristics of COP with spontaneous resolution and factors that determine the patients in whom steroid therapy might be avoided is detailed in this study.